Normally, the transmission mode of a bicycle is to transmit through the sprocket of the front pedal, by means of the chain, to the sprocket assembly at the rear axle so that the rider can tread upon the pedal to drive the bicycle forward, but in order not to affect the forward action during the stopping and counter-rotation of the pedal, a free wheel Rotary Body is installed at the rear axle where the most important part of the said Rotary Body is to have a clutch with an one-way brake which possesses brake-driving effect to drive the wheel when the rider is pedaling and it will not affect the wheel rotation when the rider is not pedaling or in back-pedaling. The free wheel Rotary Body structure of a bicycle of the currently known prior art, based on this kind of transmission mode, has the following two types which will be depicted, with their advantages and disadvantages, as follows:
1. Referring to FIG. 1, the main components of the first type comprise: a free wheel housing 1, a free wheel kernel 2, a steel ball top cover 3, two sets of steel balls placed in annular shape 4 and 5 and the one-way clutch installed in the free wheel kernel 2; the one-way clutch is consisted of a pair of ratchet pawls 6, a c-spring and a ratchet teeth groove 8 with the free wheel ratchet pawl 6 fitted on the float on the ratchet pawl bearing 9 of the kernel by means of the c-spring and to make the ratchet pawl 6 have a rotational clearance with a small angle in the bearing 9; the ratchet pawl 6 can catch the ratchet teeth groove 8, which is in the inner side of the free wheel housing, to have brake-driving effect whenever there is a rotation in certain direction between the free wheel housing and the kernel; while the ratchet teeth groove 8 can press the free wheel ratchet pawl to recess into the bearing 9 of the free wheel kernel to rotate, thereby, it allows rotation in only one direction. Referring to FIG. 2, when the rider performs pedaling, back pedaling and re-pedaling, i.e., the one-way clutch of the free wheel kernel goes through the process of brake-driving, recessing to rotate and re-brake-driving, the largest possible idle pedaling interval is an angle (theta) of a ratchet tooth, in case the theta angle is too large, it is apt to cause power output delay, also, the relative velocity between the ratchet teeth and the ratchet pawl will be excessively large which will result in excessive impact forces that not only lowers the service life of the overall structure but also affects the riding comfort ability and safety; the improvement, under this condition, tends to reduce the interval (the angle theta of ratchet teeth) of idle pedaling, one way of attaining this is to try to increase the ratchet teeth number in order to decrease the ratchet teeth angle but considering the fact that the provision of sufficient brake-driving force between the ratchet teeth and ratchet pawl needs sufficient teeth depth and also the increase of teeth number will result in the decrease of teeth depth under the original diameter, therefore, one can not simply increase the teeth number while neglect the derivative negative-effect in order to improve the above mentioned situation. PA0 2. Referring to FIG. 3, in addition to the components included in the first type, the second type comprises an extra set of one-way clutch and the two sets of one-way clutches are installed on the same plane in the kernel with an interval of a phase difference, that is, it needs to establish, in the same kernel, two sets of ratchet pawl bearings 9 corresponding to each other, under this premise, it will not only increase the manufacturing cost but also affect the strength of kernel 2, and the influence will become even prominent, especially when the free wheel needs a small diameter. In addition, one must consider the fact that current trend of bicycle development is to increase the range of speed variation which lies in the lowering of the teeth number of the sprocket assembly which are meshed around the free wheel housing, that is, when the teeth number is reduced, the forwarding velocity of the bicycle will increase, but the reduction of the teeth number will cause the diminishing of the sprocket assembly accordingly; in order to assure the sufficient strength of the small sprocket assembly, it is better to keep the internal hole, where sprocket assembly meshed with the spline on the free wheel housing, as small as possible, hence, free wheel with small diameter is the target to endeavor nowadays; under this tendency, the diminished diameter of the housing will result in the reduction of the number of the internal ratchet teeth, thereby, will cause the increase of the interval of the idle pedaling (theta increase) accordingly as the first type of structure mentioned above, which only get into the situation of "taking care of one and losing hold of the other", and the second type of structure as aforesaid will seriously affect the strength of the kernel, therefore, on the development of free wheel with small diameter, there are bottlenecks which are hard to break through in both the first type and second type of structure. In view of this, the inventors, accumulated their long time experience and through their persistent research on the design, finally developed a Rotary Body structure of the free wheel which not only can raise the reliability of the overall structure and service life but also can be applied in free wheel with small diameter without affecting the strength of the structural assembly of the kernel and the one-way clutch, thereby, greatly improve the shortcomings of the prior art, and by means of that, to accommodate the trend of future development to attain the object of expanding the range of speed variation, and this is the aim of design of the present invention.